My tap water has a pH of 8.2. I have zebra danios, an angel fish, a swordtail, a female betta, and some cories that have all adjusted to the high pH. I now have available to me some purified water that, when combined with equal parts of my tap water, will result in a pH of 7.4. The new water has been proven to be safe for fish and the water would not rebound since this is not an additive.

My question, though, is whether or not it is worth it to slowly lower the pH since the fish are now used to the higher pH. Would I possibly kill some of the fish by doing so, or is the lower pH so much better for the fish that it would be worth the hassle and headache?

Depends. Some fish, especially at this time of year, are wild cought from the southern lattitudes. They are used to their native, softer water. You will need to make the call. You are the one observing their behavior. If they begin to stress, make the changes. If not, I'd leave well enough alone.

I am inclined to think that leaving them alone is best. I have had all of them for nearly a year now, they have vibrant colors and are quite spunky. All are tank-raised locally and none are imported. I've long wanted to try discus sometime, so if I ever set up a discus tank I might give the half-and-half water a try.